The proposed research will investigate the origin and conduction of excitation in vascular muscle. Intracellular and extracellular stimulation of groups of vascular muscle cells in different morphologies as they occur in cell culture will be used to identify the electrical basis for cell interaction. Intercellular communication will be studied by the injection of fluorescent dyes into one cell and the quantitation of movement of fluorescence from that cell to neighboring cells. The structures involved in the cell-to-cell coupling will be studied by the use of freeze-fracture electron microscopy. Alteration of neurotransmitters and ionic environment will be used to modulate the contact between vascular muscle cells to study the mechanisms responsible for formation and breakdown of cell communication. The mechanism of development of high sensitivity to neurotransmitters will be studied by electrophysiological measurements of cell membrane properties. The effect of innervation on the formation of cell contacts and degree of interaction among cells will be determined by innervation of the vascular muscle cells in culture with sympathetic chain added to those cultures. The combination of electrophysiological, differential interference (Nomarski) light microscopic, and ultrastructural measurements will allow a comprehensive description of the mechanisms coupling the activation of vascular muscle cells.